1. Field
The present disclosure relates generally to aircraft and, in particular, to a method and apparatus for controlling aerodynamic performance of an aircraft. Still more particularly, the present disclosure relates to a method and apparatus for changing the shape of a control surface for an aircraft.
2. Background
An aircraft is a type of vehicle capable of flying through the atmosphere. Aircraft may include fixed-wing aircraft and rotor craft. The flight of an aircraft may be controlled by a number of flight control surfaces. A flight control surface is a part of the surface of an aircraft that may control the aerodynamic performance of an aircraft. A flight control surface may be used to adjust or control the attitude of an aircraft. The shape and/or position of flight control surfaces may generate lift, control stability, change direction, change drag, and/or change other suitable aerodynamic parameters for an aircraft.
Flight control surfaces on an aircraft may be used to change the direction of an aircraft around three axes. These axes include a vertical axis, a longitudinal axis, and a lateral axis. A vertical axis passes through an aircraft from top to bottom. Rotation or movement about this axis is called yaw. Yaw changes the direction of the nose of an aircraft pointing it to the left or right. The longitudinal axis passes through the aircraft from the nose to the tail. Rotation about this axis is referred to as bank or roll. The lateral axis passes from one wing tip of an aircraft to another wing tip of an aircraft. Rotation about this axis is referred to as pitch.
Control surfaces may include, for example, an aileron, an elevator, a rotor, a trim, a rudder, a spoiler, a flap, a slat, a thrust reverser, and/or other suitable control surfaces. Different control surfaces may be attached to an airfoil to provide for different axes of motion for the aircraft. An airfoil may be a wing or a blade of an aircraft. These control surfaces may be used to optimize the aerodynamic surfaces of an airfoil.
For example, a flap may be located at a trailing edge of an airfoil in the form of a wing. A flap is an extension to the back of a wing to provide lift augmentation as well as drag augmentation. Further, deployment of a flap may reduce the stalling speed for an aircraft by altering airflow over the wing. Flap deployment may allow an aircraft to climb and/or descend at a steeper angle without an increase in speed. Movement of this type of control surface, as well as other control surfaces, during flight may be performed to maximize the handling and performance of the aircraft.
When deploying a flight control surface, it is desirable to have a control surface that may remain straight in an undeployed configuration but may have a high degree of flow turning in a deployed configuration. The degree of flow turning for a control surface is the degree at which airflow over a wing may be turned or deflected with respect to the original direction of airflow. For example, the deployment of a flap may cause the airflow over a wing during flight to be deflected at some downward angle with respect to the original direction of airflow. Further, it is desirable to have a first side of a control surface that curves in a smooth manner. In other words, the control surface does not have sharp discontinuities in the slope of the first side when in a deployed configuration. It is also desirable to have control surface shape changing systems that do not have protrusions in the mold line of the control surfaces or the aircraft parts to which they are attached.
Currently, existing control surfaces include extension and/or unfolding mechanisms that have protrusions. For example, currently used flap systems may have fittings which protrude into the airstream on a second side of a wing. Some existing control surfaces may use sliding joints to lengthen the first side of a control surface and shorten the second side of a control surface during deployment of the control surface. Further, some control surfaces may also use a sliding joint at the tip of a control surface. These control surfaces may have inadequate strength, may be heavy, and/or may be expensive.
The types of changes to the shape of a control surface that may be made with existing flight control surfaces may be limited and may not provide desired aerodynamic performance. For example, existing flap systems do not allow for a high degree of flow turning. A high degree of flow turning may be direction of airflow at the tip of a deployed flap and may be greater than around 50 degrees inclined to the horizontal plane of the aircraft.
Therefore, it would be advantageous to have a method and apparatus that addresses at least some of the issues discussed above and possibly other issues.